1. Field of the Invention
The present invention relates to an enhanced flex cable, used to electrically couple a fiber optic data communications transceiver, for example, to an associated wiring board.
2. Background Information
An optical transceiver is a device that uses pulses of light to carry signals for transmitting and receiving data at very high speeds. Typically, the light pulses are converted into, or converted from, associated electrical signals using known circuitry. Such optical transceivers are often used in devices, such as computers and data communication networks, in which data must be transmitted at high rates of speed.
Optical transceivers typically use an optical transmitter, such as a light emitting diode (LED) or laser, for example, to transmit the light pulses, and/or an optical receiver, such as a photodiode chip or photo detector chip (hereinafter receiver chip), for example, to receive the light pulses. One type of optical transceiver has a subassembly including a receiver chip disposed within a transistor-outline (TO) can package. This type of optical transceiver subassembly is known as a receiver optical subassembly (hereinafter ROSA for short). Another type of optical transceiver has a subassembly that includes either an edge-emitting laser or a surface-emitting laser, such as a VCSEL, disposed within a TO can package. This type of subassembly is known as a transmitter optical subassembly (hereinafter TOSA for short). The specifics of ROSAs and TOSAs are well known to those skilled in the art. However, briefly, the TO can package is a metal housing that hermetically houses the other components of the ROSA or TOSA. The TO can package may then be disposed within a further housing, formed of a plastic for example, that is adapted to couple a ferrule or optical fiber to the receiver chip or laser.
Typically, the ROSA and TOSA are electrically coupled to a printed circuit board (also known as, and herein after referred to, as a transceiver wiring board). The transceiver wiring board includes the associated electronics for operating the receiver chip or laser. These electronics include, for example, the laser driver and control, receiver preamplifier and post amplifier, and other supporting components. In a computer system, the transceiver wiring board is typically connected to a further circuit board, for example, a motherboard. The assembly may then be positioned within a chassis, which is a frame fixed within a computer housing. The chassis serves to hold the assembly within the computer housing.
Typically, the TOSA and ROSA are electrically coupled to the transceiver wiring board using a number of relatively rigid leads. For example, the aforementioned ROSA conventionally has four leads: a power lead for supplying power to the ROSA; a single ground lead for connecting the ROSA to a ground potential; and two data leads for transmitting signals to and/or from the ROSA. The TOSA also conventionally has a number of leads for coupling the laser within the TO can to the transceiver wiring board. Each of the respective leads typically extends out of the TO can for connection to the transceiver wiring board in a known manner, and in an industry standard arrangement. For example, the ends of the respective leads may be passed into corresponding vias formed in the transceiver wiring board, and soldered in place. Alternatively, the ROSA/TOSA leads may be connected to the transceiver wiring board by soldering the leads to electrical pads on the bottom or top surface of the transceiver wiring board.
However, this manner of connecting the leads to the transceiver wiring board requires that each of the leads has a relatively long length. The long lengths have generally been deemed necessary in order to allow the ROSA/TOSA to be properly oriented relative to the transceiver wiring board, while still allowing the ROSA/TOSA to be connected thereto. That is, the leads typically extend out of a rear portion of the ROSA/TOSA and initially in a direction parallel to the surface of the transceiver wiring board. Thus, in order to connect the leads to the transceiver wiring board, the leads must also extend for a distance in a different direction, i.e., toward the transceiver wiring board. Depending on the orientation and geometry, the length of the leads may be so long as to cause the leads to disadvantageously have a relatively high impedance. As is known to those skilled in the art, a high impedance on the leads is undesirable, since this may affect the immunity of the receiver, for example, to noise present on the power supply or ground. Moreover, this configuration may subject the leads to a cross talk (i.e., undesirable coupling) effect. Thus, there is need for a way to easily and rapidly electrically couple the leads of a ROSA and/or TOSA, for example, to a transceiver wiring board, while reducing the impedance, and minimizing the cross talk effect. Furthermore, due to the industry-standard arrangement of the optical transceiver utilizing a ROSA and/or TOSA, the ROSA and/or TOSA are typically placed immediately adjacent to an edge face of the transceiver wiring board, with the ground lead typically extending from the TO can at the edge face (i.e., between the upper and lower primary surfaces of the transceiver wiring board). The transceiver wiring board is thus conventionally provided with a notch to accommodate the ground lead. However, this requires that the ground lead be provided with a relatively long length and numerous bends to allow the ground lead to pass past the notch and to allow the ground lead to be connected to the transceiver wiring board in the aforementioned manner. Alternatively, it is also known to provide a ground cage that can be connected to the ground lead and to a ground potential. For example, the ground cage can be attached and grounded to the transceiver wiring board, which may in turn be fastened to, and grounded in a known manner, to the motherboard and its ground. While this may allow the length of the ground lead to be reduced, it also requires the use of a further component (i.e., the ground cage), which increases inventory costs. Moreover, connecting the ground cage to the ground lead and to the transceiver wiring board is a labor intensive procedure.
According to one aspect of the invention, a flex cable is used in conjunction with a so-called duplex optical transceiver. The duplex optical transceiver has a so-called electro-optic receiver optical subassembly (ROSA) positioned adjacent to a transmitter optical subassembly (TOSA). In the exemplary embodiment, the ROSA has four leads projecting from the rear surface of a respective transistor-outline (TO) can package: a power lead for supplying power to the ROSA; a ground lead for connecting the ROSA to a ground potential; and two data leads for transmitting signals to and/or from the ROSA. The TOSA may be similarly tailored, or have a different configuration. However, in the exemplary embodiment, the TOSA has three leads projecting from the rear surface of a respective TO can package: a power lead for supplying power to the TOSA; a cathode lead; and a monitor lead. However, the present invention may be used with electrical components having more or fewer leads without departing from the spirit and scope of the invention.
The exemplary flex cable is used to electrically couple the leads of the ROSA and TOSA to a transceiver wiring board. The transceiver wiring board includes the associated electronics for operating the ROSA and/or TOSA, for example the laser driver and control, receiver preamplifier and post amplifier, and other supporting components.
In accordance with industry standards, the ROSA/TOSA are placed immediately adjacent to an edge face of the transceiver wiring board. Moreover, due to industry standards, the ground lead of the ROSA, for example, extends from the TO can package in a region of the edge face of the wiring board (i.e., between the upper and lower primary surfaces of the transceiver wiring board). To accommodate the ground lead, the edge face of the transceiver wiring board is provided with a notch. Thus, the ground lead projects into the space formed by the notch.
The leads of the ROSA and TOSA are advantageously electrically coupled to a transceiver wiring board using the flex cable. In the exemplary embodiment, the flex cable has a relatively flat configuration, and is relatively flexible to allow the flex cable to be bent at an angle. The term xe2x80x9cflexiblexe2x80x9d means that the cable can be bent into a desired shape.
In the exemplary embodiment, the flex cable has two superposed conductive layers, such as copper layers, separated from each other by an insulating layer, such as a polyamide material.
In this exemplary aspect of the invention, the conductive layers are patterned, in a known manner, so that one of the conductive layers includes a ground layer which will serve to couple the ground lead of the ROSA, for example, to the ground potential.
The exemplary flex cable has the outer surfaces of the respective conductive layers coated with an insulating material, such as a polyamide film, to ensure that the conductive layers do not inadvertently become shorted.
One end of the flex cable is attached to the ROSA/TOSA, so that the respective leads are electrically coupled to the respective conductive wirings of the flex cable. In the illustrated exemplary embodiment, the respective leads are severed, to form relatively short stumps. As such, the disadvantages associated with long, exposed leads are eliminated. Moreover, the flex cable may have a plurality of holes formed therein, for receiving the respective lead stumps. In this aspect of the invention, the holes are formed in predefined locations to provide access to the respective conductive wirings. Thus, when the lead stumps are inserted into the respective holes, the respective conductive wirings can be electrically connected, for example using soldering techniques, to the respective leads.
In this exemplary aspect of the invention, the holes may be plated with a conductive material. The conductive material is in contact with the respective wiring accessible by way of the hole, and serves as an interface between the respective lead and the conductive wiring.
The opposite end of the flex cable may have portions of the insulating material removed, to expose portions of the respective conductive wirings. These exposed portions can then be coupled, for example wire bonded, to the respective signal, ground and/or power traces on the upper surface of the transceiver wiring board. Thereafter, the various electrical connections can be coated to protect the connections and wirings from being damaged.
In an exemplary aspect of the invention, the flex cable is bent at an angle, for example a 90 degree angle. This bend allows the flex cable to advantageously follow the transition between the back of the TO can, where the leads are located, and the surface of the transceiver wiring board. Thus, the flex cable replaces the extra length of the conventional leads that was previously needed to form the connection.
In an alternative exemplary aspect of the invention, the flex cable may be configured to allow it to be connected to an underside of the transceiver wiring board. For example, the flex cable may be bent at a 90-degree angle, so that a vertical portion of the flex cable can be attached to the leads of the ROSA/TOSA, and the horizontal portion of the flex cable can be attached to the underside of the transceiver wiring board. This aspect of the invention frees up the upper surface of the transceiver wiring board for the placement of electronic components, and/or to allow for the further miniaturization of the wiring board. Moreover, this aspect of the invention may facilitate assembly of the arrangement, especially when the upper surface of the transceiver wiring board has other features disposed thereon, which may prevent the attachment of the flex cable to the upper surface.
In all aspects of the invention, the surface of the transceiver wiring board may be provided with contact pads in electrical communication with the respective signal, ground and/or power traces. The exposed portions can be directly connected to the respective contact pads, to allow the wirings of the flex cable to be electrically coupled to the respective signal, ground and/or power traces of the transceiver wiring board.
In another exemplary aspect of the invention, the flex cable is provided with a grounding tab that is electrically coupled to the ground layer, and which is adapted to be connected to the ground lead. For example, the grounding tab can simply be a flap that is punched from or cut into the flex cable. The ground tab, in this exemplary aspect of the invention, has a portion of the ground layer therein, and has a hole that accommodates the ground lead to allow for communication with the ground wiring, similar to the holes discussed above. Thus, when the flex cable is attached to the upper surface of the transceiver wiring board, the grounding tab can be used to project into the notch of the transceiver wiring board, and coupled with the ground lead. To facilitate this coupling, the interface (i.e., point of connection) between the grounding tab and the remaining portion of the flex cable is disposed at a junction where the flex cable is to be bent at an angle to accommodate the transition between the vertical surface of the TO can package and the upper surface of the transceiver wiring board. Thus, when the flex cable is bent to allow its connection to both the upper surface of the transceiver wiring board and the leads of the ROSA/TOSA, the grounding tab will be disposed in a vertical direction, allowing its direct connection to the ground lead. Moreover, this will also cause a flap opening to form in the flex cable, which is disposed at least partially in the radius of the bend of the flex cable. The flap opening will allow access to the ground lead from a direction of the upper surface, so that the ground lead can be soldered, for example, to the grounding tab.
Likewise, when the flex cable is attached to the lower surface of the transceiver wiring board, the flap opening will allow access to the ground lead from a direction of the lower surface, so that the ground lead can be soldered, for example, to the grounding tab. This is especially advantageous when the upper surface of the transceiver wiring board has features that may prevent access to the lead from the direction of the upper surface, and when the flex cable is pre-attached to the lower surface. Moreover, the grounding tab can be tailored to lay flush against the back of the TO can in a region of the ground lead, even if the flex cable is curved in this region. Thus, this configuration prevents stress in the flex cable, and in the respective electrical connections between the leads and the flex cable.
In an alternative aspect of the invention, the grounding tab may be a separately formed feature that is attached to the underside of the flex cable, for example, and electrically coupled to the ground layer. Similar to the previously described embodiment, this aspect of the invention has the grounding tab disposed at the junction where the flex cable is to be bent at an angle. A separate through hole may then be formed in the flex cable to provide access to the ground lead, in a manner to the flap opening, as discussed above.
The flap opening formed in the flex cable also helps to allow the flex cable to be bent into its desired shaped. By forming the grounding tab at the junction where the flex cable is to be bent, the workability of the flex cable is enhanced. Moreover, in another aspect of the invention, it is also contemplated that the grounding tab be provided solely to enhance the bendability of the flex cable. In this aspect of the invention, the tab (if provided) is not necessarily electrically connected to the wirings of the flex cable. Moreover, it is further contemplated that instead of a tab, through holes may be formed in the flex cable to enhance its flexability.
Moreover, it is contemplated that a conductive tab tailored in the manner of the above-described grounding tab could be electrically coupled to other conductive layers or wires of the flex cable, such as the signal layer or wires, or the power layer or wires, for connection to other respective leads, for example.
In another aspect of the invention, a stiffener plate may be disposed adjacent to an end of the flex cable that is connected to the transceiver wiring board. The stiffener plate provides support for the flex cable, to help ensure the connection between the flex cable and the transceiver wiring board is maintained. Moreover, if the stiffener plate is formed of a heat conductive material, such as aluminum, heat generated from an external source may be intentionally conducted via the plate into the interface between the flex cable and the transceiver wiring board. This heat can be used to cause solder located at the interface to reflow, to help form the electrical connection.